Radiation therapy involves aiming radiation at a tumor from one or more directions. In some radiation therapy systems, the radiation source mounted on a gantry rotates around a patient on a table or couch, and directs radiation toward the patient's tumor(s). As the radiation source rotates around the patient, the patient table or couch may be moved in a direction that is parallel to the axis of rotation of the radiation source. In this manner, radiation may be applied to the patient's tumor(s) from various gantry angles and at various patient table or couch positions, based on images of the patient and the tumor(s) generated by various imaging modalities in advance of the treatment session.
Emission-guided radiation therapy (EGRT) applies radiation based on positron emission paths emitted by a positron emission tomography (PET) tracer that are localized to the tumor(s) during the treatment session. In addition to a radiation source to therapeutically irradiate a tumor region, an EGRT system also has an array of PET detectors to sense positron emission paths that originate within the tumor region, which may provide real-time location data. This may reduce the latency between the localization of a tumor and irradiation to that tumor. In order to timely respond to the detection of a positron emission path that indicates the real-time location of a tumor, the gantry of an emission-guided radiation therapy system may rotate at speeds ranging from about 10 rotations per minute (RPM) to about 70 RPM. Improvements to the gantry rotation mechanisms, the radiation source, and/or radiation sensors (e.g., PET detectors, gamma ray or X-ray detectors, etc.) may be desirable in order to accommodate this increased gantry rotation speed. Conversely, an increase in time resolution in the PET detectors may decrease the required rotational latency due to the confined spatial extents of the PET events that are coupled to the time resolution of those events.